Project Summary: Anti-NMDA receptor encephalitis is a potentially lethal encephalitis attributed to autoantibodies against the N- methyl-D-aspartate receptor (NMDAR). Patients with anti-NMDAR encephalitis present with psychiatric and cognitive symptoms, and then progresses to severe neurological dysfunction, including seizures, abnormal movements, impaired consciousness, and autonomic instability, frequently requiring mechanical ventilation. In spite of the severity of the symptoms, substantial recovery is possible for patients treated with immunosuppressive therapies that reduce titers of anti-NMDAR antibodies. Despite the strong correlation between patient anti-NMDAR antibodies and the clinical syndrome, the pathogenic role of anti-NMDAR antibodies in the disease has not been definitively established. Likewise, the actions of anti-NMDAR antibodies on neurons are incompletely understood. The primary obstacle to definitive study is the lack of pure anti-NMDAR antibodies cloned from patients. Prior studies have been restricted to the limited amounts of polyclonal antibodies obtainable from patient sera and CSF. Monoclonal anti-NMDAR antibodies obtained from patients would, for the first time, allow demonstration that the pathophysiological events believed to underlie anti-NMDAR encephalitis are attributable to anti- NMDAR antibodies alone. The antibodies would enable study of how they affect glutamatergic signaling in the brain, facilitate the development of animal models for anti-NMDAR encephalitis, and permit structural modeling of the antibody-NMDAR complex, which could then direct the design of targeted therapies. Our hypothesis is that, in anti-NMDAR encephalitis, antibodies to the extracellular region of the NMDAR lead to internalization of receptors on neurons, leading the NMDAR hypofunction. Our primary objective is to test this hypothesis by cloning antibodies from patients with anti-NMDAR encephalitis and using them to understand the properties of this disease. We will collect B-cells from patients with anti-NMDAR encephalitis, clone their antibodies, and characterize their NMDAR binding properties and effects on receptor function. These experiments will establish whether anti-NMDAR mAbs have features consistent with a primary role in disease pathogenesis. They will lay a foundation for definitive experiments in animal models as well as structural studies to delineate the molecular structure of disease-related immune complexes. 1